Tango of Titans: Centaurus A and M83 as a Local Group Analog

TL;DR

This paper demonstrates that the Centaurus A and M83 galaxy pair is dynamically similar to the Milky Way and Andromeda, using the Timing Argument and simulations to estimate their total mass and interaction state.

Contribution

It introduces a novel application of the Timing Argument calibrated with simulations to estimate the mass of the Centaurus A/M83 system, establishing it as a Local Group analog.

Findings

Estimated total mass of the system: (6.36 ± 1.30) × 10^12 solar masses.

CenA and M83 are infalling and interacting, similar to the Milky Way-Andromeda pair.

The mass estimate aligns with independent virial and luminosity-based measurements.

Abstract

Centaurus A (CenA) and M83 form one of the most massive galaxy pairs in the nearby Universe. Although their observed heliocentric velocities suggest motion that is not obviously indicative of mutual attraction, this work presents evidence that CenA and M83 are in fact infalling toward each other, exhibiting a dynamical interaction analogous to the binary-like motion of the Milky Way and Andromeda in the Local Group (LG). Using the Timing Argument (TA), calibrated with analog galaxy pairs from the AbacusSummit simulation, we estimate the total mass of the CenA/M83 system under the assumption that the line-of-sight (LoS) velocity is dominated by motion toward the system's barycenter. This yields a total mass of $(6.36 \pm 1.30) \cdot 10^{12}\, M_\odot$. The inferred mass agrees well with independent estimates based on virial mass measurements and $K$-band luminosity--to-mass ratios. Together, the consistent bound signature and robust mass determination highlight the CenA/M83 system as a compelling nearby analog to the LG. Further discussion of NGC 4945 as a main perturber (as the Large Magellanic Could) for the CenA is also discussed.